1. Field of the Invention
The present invention generally relates to lens systems for near infra-red imaging devices.
2. Description of Prior Art
With recent advances in charge coupled device (CCD) camera technology, it is now possible to fabricate focal plane detector arrays which are sensitive in the 1.5 to 2.55 micron spectral region. This spectral region features relatively good atmospheric transmission, and can capture energy from both reflective and thermally emissive objects at normal terrestrial temperatures. Most commercially available CCD camera lenses and night vision optics are optimized for use with wavelengths in the 0.6 to 1.0 micron band, and are not suitable for use with wavelengths in the 1.5 to 2.55 micron band. The lens materials are too lossy in the latter band and the corrections for chromatic and spherical aberrations are inadequate